Urban Ecology

Planting Trees, Redeeming Lives

The Rise of Urban Ecology

This idea of using trees to remake cities and neighborhoods on more natural lines reflects a modern urban ecology movement that got its start one fall day in 1988. An F&ES professor named Bill Burch had just delivered a talk about the community-based forestry program that he was helping to develop in rural Nepal, when a member of the audience, Ralph Jones, demanded, “Why are you not doing that here in our cities?” Jones had just become director of Baltimore’s recreation and parks department, and the two men quickly came to an agreement. Soon after, Morgan Grove, a student in Burch’s community forestry class, got the word: “You’re going to Baltimore.” Burch remembers posing the proposition more diplomatically: “Boy, do I have an offer!” He promised Grove and other F&ES interns who followed that “they would learn more about participatory forestry and how it all works” in three months in Baltimore than “in 10 years in the Mt. Hood National Forest,” and he adds now, “I was right.”

Dana Keeton
Bill Burch promised his students that “they would learn more about participatory forestry and how it all works” in three months in Baltimore than “in 10 years in the Mt. Hood National Forest.”

Burch became the first director of the new Urban Resources Initiative (so called “because the president of Yale at that time did not want any more institutes”), and his students were soon collaborating with city staff and community groups to develop the first strategic plan for Baltimore’s parks. Participatory forestry meant getting local people invested in improving their own neighborhoods. So among other early efforts, URI interns helped enlist youth groups to clean up and restore the 14-mile-long Gwynns Falls-Baltimore greenway. They also developed the city’s first neighborhood tree steward program. In 1991, URI added a New Haven counterpart to its efforts in Baltimore. The idea in both cities, says Burch, “was to use natural resources as a means for rebuilding neighborhoods that had lost most of their social capital, only we did not have that buzzword available then.” At a time when other scientists scarcely thought of cities as ecosystems at all, URI brought an interdisciplinary team of social scientists, foresters and hydrologists to bear on urban neighborhoods, with a dual emphasis on people and watersheds. Burch wanted to get past the image of parks as “elitist conceits.” Instead, the parks, together with improved street plantings and rehabilitated vacant lots, would be the means for simultaneously addressing issues ranging from community spirit to the state of local waterways.

“The idea was to use natural resources as a means for rebuilding neighborhoods that had lost most of their social capital.” Bill Burch

It was the beginning of a move away from old-style “urban forestry.” That term had been around since the late 19th century and gained currency in the 1960s after Dutch elm disease raised public awareness of the importance of city trees (and cost New Haven its reputation as the “Elm City”). The U.S. Forest Service had started paying attention to urban areas for the first time in the 1970s. But the result was at best a holding action—underfunded, narrowly focused on improving municipal maintenance of street trees and utterly overwhelmed by the rapid pace of urban change. By the late 1980s, the average city was losing four trees for every one it planted, according to a study by the conservation group American Forests. The average life of a downtown street tree was just 13 years. Even after a sharp rise in U.S. Forest Service spending for cities, up from about $2 million a year in the 1980s to as much as $25 million in the 1990s, the results continued to be frustrating, according to Gary Moll of American Forests. Only a few states had urban forest councils, and funds tended to get widely dispersed without much thought about where tree planting could produce the biggest benefits. That’s now changed, says Moll, with the U.S. Forest Service holding back a substantial portion of funds to award on a competitive basis “to a few great projects.” But he figures that cities are still losing three trees for every one they plant.

The shift from thinking about urban forests to urban ecology happened in the late 1990s. Grove had gone to work for the U.S. Forest Service in Baltimore in 1996, the day after defending his doctoral thesis at Yale. Federal officials soon began looking at URI’s work in Baltimore as a model. The Forest Service had customarily funded long-term research (LTR) projects in natural settings around the country. But it had never attempted such an ecosystem study in a city—and wasn’t all that keen on trying. (Some old-school Forest Service types still kid Grove about his job title—research forester: “You’re a social scientist. Get out!”) But the work begun by URI in Baltimore demonstrated that you “could really do” serious ecosystem research in a city, says Grove, using standard scientific tools like vegetation study plots, forest inventories and hydrology. In 1998, the National Science Foundation (NSF) agreed to fund the nation’s first urban long-term research sites in Baltimore and Phoenix. And once the NSF had conferred legitimacy on the field, ecologists finally began to think that such a thing as urban ecology might actually exist.

Urban forests, it turns out, are as rich and complicated as any other forest, and possibly more so because they’ve undergone such dramatic transformations. Conventional wisdom from rural areas holds, for instance, that vegetation buffer zones along rivers and streams automatically filter out nitrates and other pollutants. But in Baltimore, an early LTR study found that urbanization had changed the hydrology so much that polluted runoff was traveling below the root zone of riparian trees and reaching waterways unfiltered. “That was a big ‘Aha!’ moment for policymakers,” says Grove. They switched the focus for tree planting from riparian zones (the endpoint for runoff) to the city-at-large (the source) as a more effective way of dealing with both the quality and quantity of runoff, and they set a goal of doubling Baltimore’s tree canopy cover to 40 percent.

Studies in Baltimore and other cities also turned up surprising pockets of biodiversity, sometimes including rare or endangered native species. (The discoveries included a new earthworm species in Baltimore, and a German study found more native plant diversity in one city than in nearby rural areas.) An LTR ecologist, Paige Warren of the University of Massachusetts, is now working on a theory that 35 percent canopy cover is a threshold at which a Northeastern U.S. city can start to see more woodpeckers and other forest birds, rather than just the drab urban generalists like sparrows and pigeons. She’s developing guidelines to encourage this transition by keeping some dead trees and branches intact in areas where they don’t pose a hazard to residents. Despite the perception that having songbirds in the backyard is a “luxury good” of little relevance to people living on the poverty line, the LTR researchers found that residents in poor areas are well aware of what they’re missing. Like their counterparts in leafier neighborhoods, says Warren, “they’re more satisfied with places that native birds are more satisfied with.”

But the new urban ecologists have also found that deciding how and what to restore is rarely simple. It isn’t about bringing back the forest primeval. In New York City, for instance, “million-tree” planners have had to omit many of the original native tree species because they are susceptible to introduced Asian longhorned beetles. The new trees must also do obvious, but unnatural, stuff like thrive in areas where the soil is compacted or tightly hemmed in by concrete. Moreover, it isn’t enough for city trees merely to look pretty. Like city people, they’re under increasing pressure to multitask, delivering a variety of “ecosystem services” beyond biodiversity. The right trees planted in the right places can shade buildings in summer and reduce energy demand. But done wrong, the planting can have the opposite effect. Likewise, trees can help reduce pollution by pulling components of smog out of the air. But certain trees, like eucalyptus and oak, produce volatile organic compounds to defend themselves—and in some settings they can actually make the smog problem worse. With those kinds of complications in mind, NSF and the U.S. Forest Service together are now building on the Baltimore and Phoenix studies to develop a network of nine urban LTR areas around the country.